Interstitial radiation therapy involves the placement of small radioactive seeds within therapeutic distance of a tumor site. Encapsulating radioactive material with low energy and short half life into a small seed for placement at the tumor site results in safe handling and reduces the risk of contamination of the patient or surrounding tissue with radiation.
Many individual seeds can be injected at the therapeutic site to provide constant irradiation of the tumor. Handling the many individual seeds necessary to treat a given patient is cumbersome because the seeds are small and must be loaded into a hollow needle for injection. During the implantation procedure, the seeds are injected or pushed into the tumor site as the needle is withdrawn from the site. The seeds are generally placed in a straight line relative to the tumor. Such individual seeds may tend to migrate along the residual needle track and change position relative to the tumor or treatment target. Seed migration may result in undesirable concentrations of seeds and a radiation overdose to some tissues, while also causing a reduced concentration of seeds in other areas and loss of therapeutic effect.
By connecting the seeds together by various structures prior to injection, the difficulties of seed handling and migration can be overcome. Connecting the seeds helps prevent migration around the tumor and subsequent changes in the radiation dose to the tumor.
Seeds can be connected by many structures. One method is to insert the seeds inside a nylon catheter and inject the catheter-seed combination into the treatment site. However, the nylon catheter can be difficult to place and the catheter ends are sewn next to the skin which provides a site for contamination or infection. Seeds are also placed by hand into a woven or braided absorbable suture. Loading the suture containing the seeds into the needle is time consuming. Also, the flexible suture braid tends to bend and clog the needle during implantation in the treatment site.
Horowitz (U.S. Pat. No. 4,697,575), incorporated herein by reference, describes seeds for interstitial use connected by interlocking members. The rigid needle-seed brachytherapy device of Horowitz is a non-deflecting member composed of rigid bioabsorbable polymers. The seeds are encapsulated within segments of the polymer and the segments are then physically interconnected or interlocked to form a needle. The segments have projections on one end and complimentary recesses on the opposite end. The non-deflecting seed needle maybe inserted into the treatment site alone or can be inserted into a hollow needle to assist implantation into the site. Use of the seed needle assembly is preferred because hollow needles can facilitate the transfer of cancer cells from a tumor treatment site. This configuration prevents any individual seed from migrating from the original implantation site. Also, the rigid strand can be inserted into the treatment site and broken or cut at the proper length. A rigid radioactive seed needle is, however, incapable of movement and remains fixed as the tumor or gland shrinks during the healing and treatment process.